Surface having a coating of a host multidentate ligand and a reversibly trapped lubricant

ABSTRACT

The lubricant layer according to the present invention is used in a thin film magnetic recording medium in which a solid surface sliding at a high speed is required to retain its lubricating performance and abrasion resistance for a long period of time, comprising a host-guest complex composed of a lubricant molecule as a guest molecule and a multidentate ligand as a host compound to form the complex with the guest molecule.

This is a Division, of application Ser. No. 08/313,909 filed on Sep. 28,1994, U.S. Pat. No. 5,536,577

FIELD OF THE INVENTION

The present invention relates to a lubricant layer which is a thin layerhaving a lubricating function at an interface where it is subjected to asliding contact with a solid at a high speed. More particularly, itrelates to a lubricating system in a magnetic recording medium providinga high recording density used in the information industry and the like,a magnetic recording medium such as a fixed thin layer magneticrecording disk, and a method of preparing the same.

BACKGROUND OF THE INVENTION

When a magnetic recording medium is used, the medium is rotated andaccelerated rapidly from a stationary state, whereby a lift is given toa head slider and a magnetic head is lifted. When the power is switchedoff after the use, a motor driving the medium for rotation will stop,and the head and the medium will come into contact with each other at ahigh speed and cause sliding.

A thin layer magnetic recording medium, which is a typical example ofthe magnetic recording medium providing a high recording density used inthe information industry and the like, is usually prepared by coating amagnetic metal or its alloy on a non-magnetic substrate by plating,vapor deposition, or sputtering. In actual use, it becomes abraded anddamaged by the sliding contact of the magnetic recording medium with thehead at a high speed. Its magnetic properties may be deteriorated.

As a method for solving such a problem, it has been proposed to providea protective layer and a lubricant layer on the magnetic layer in orderto make a static and dynamic friction coefficient of the medium duringthe sliding contact as low as possible and to improve an abrasionresistance. A carbonaceous layer, an oxide layer, a nitride layer, or aboride layer is employed as the protective layer. A liquid lubricant ora solid lubricant is employed as the lubricant layer. Generally, aperfluoropolyether compound, which is one of the liquid lubricants, iscoated on the surface of the medium.

In recent years, to obtain a higher recording density, it has becomeincreasingly necessary to reduce the flying height of the head and tospeed up the rotation of the medium. Thus, the substrate for medium hascome to be smoothed. The provision of the liquid lubricant layer is veryeffective in reducing the dynamic friction coefficient, as mentioned inthe above. As the thickness of the liquid lubricant layer increases,however, it has been found that a micromeniscus is formed by the surfacetension of the liquid lubricant between the head and the medium andthereby causes sticking. Hence, this indicates that the static frictioncoefficient of the medium increases and the head frequently becomesinoperative due to its adhesion to the medium.

As the substrate is smoothed in order to reduce the flying height of thehead, the liquid lubricant has a serious drawback in that theabove-mentioned sticking is very liable to occur. On the other hand, itis disadvantageous in that a sufficient durability cannot be obtainedwhen the thickness of the liquid lubricant layer is reduced to preventthe sticking. Further, as the rotation speed of the medium increases,there occurs a marked phenomenon called "spin-off" and the thickness ofthe lubricant layer is reduced. To avoid such phenomena, the search hasgone on for a solid lubricant which does not form the meniscus and ithas been proposed to use a higher alcohol, a higher fatty acid, or metalsalts thereof.

The solid lubricant has a problem, however, in that, when it is coatedon the magnetic layer, a crystallization is liable to take place in partof the coated layer which causes a cohesion, since its stable phase isas a solid at the ambient temperature. In particular, the tendencytoward cohesion is marked when the substrate is smoothed. When thecohesion occurs, the thickness of the coated layer becomes uneven, whichincreases the possibility that the head will be brought into directcontact with the magnetic layer of the medium. In addition, a stain mayform on the head slider or the flying height of the head may be madeunstable. In order to prevent the cohesion of the solid lubricant and toprevent the spin-off, it is necessary to effectively bind and cause themolecules of the solid lubricant to adhere to the substrate. Oneapproach that has been proposed to increase the bonding strength of themolecules of the lubricant has been a method of polymerizing analkylsilane (Japanese Unexamined Patent Publications No. 103721/1990 andNo. 103722/1990). However, according to this method, the lubricant ispolymerized, whereby the movement of their molecules is restricted andthe lubricating performance becomes inadequate. This is because there isa trade-off to be made between the fixation of the lubricant and itslubricating performance.

Further, even though the solid lubricant exerts a good lubricatingperformance in the initial stage, the friction coefficient markedlyincreases with the passage of time and no satisfactory lubricatingperformance can be obtained. The higher fatty acid, which has the effectof fairly maintaining the friction coefficient at a low level, has thedisadvantage of becoming easily liquefied under the conditions in whichit is brought into contact with the head at 50° C. or higher because itgenerally has a low melting point and therefore has a tendency to causethe sticking of the head. On the one hand, to avoid such a disadvantage,it has been proposed to use the higher fatty acid in the form of a metalsalt which has a higher melting point (e.g., Japanese Unexamined PatentPublication No. 281220/1988). The metal salt of higher fatty acid has agood lubricating performance. On the other hand, it has a drawback inthat its solubility in a common organic solvent is poor and thus itscoating possibilities are limited. In addition, there are problems inthat an even coated layer is hardly obtained when the metal salt iscoated on the medium and the thickness of the coated layer isconsiderably uneven. This tendency toward unevenness is particularlymarked when the substrate is smoothed, which may possibly lead toserious results such as a head crash.

A reversible adhesion is ideal as a fixation system in which thelubricant molecules interact with the substrate while retaining thestrength enough to prevent the cohesion and the adhesion does not use atrade-off with the lubricating performance.

An object of the present invention is to obtain a lubricant layer whichis a thin layer but which has an excellent lubricating performance andis free from the cohesion of the lubricant molecules, that is, alubricant layer excellent in durability without introducing a trade-offbetween the adhesion of the lubricant and its lubricating performance.The present invention has been achieved by designing the lubricatingsystem at a molecular or atomic level. The present invention alsoprovides a magnetic recording medium having an even and thin lubricantlayer which is excellent in lubricating performance and durability andwhich is formed by using the above lubricant layer.

SUMMARY OF THE INVENTION

More specifically, in the lubricant layer of the present invention, thelubricating molecule, which is the guest molecule, is trapped by thehost compound adhering to a solid substrate through electrostaticinteraction such as an ionic bond so that the lubricant molecule can befixed to the solid substrate with a good orientation and its manner ofbonding can be made reversible. Therefore, there has been achieved notonly the prevention of the cohesion of the lubricant but also theprovision of a more excellent durability and lubricating performance.

The lubricant layer of the present invention can be applied to varioussolid surfaces including, for example, polymer, carbon, oxide, nitride,boride, and metal. Thus, it can be widely applied to any solid surfaceirrespective of its nature as long as the host compound can be adheredthereon.

The flying height of the head can be reduced when the lubricant layer ofthe present invention is applied to the surface of the magneticrecording medium. Hence, it is possible to enhance the recording densityof the magnetic recording medium and to construct a magnetic recordingsystem which will remain reliable for a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the lubricant layer of the present invention applied to amagnetic recording medium.

FIG. 2 shows an 18-crown-6 derivative and potassium stearate forming ahost-guest complex and the complex adhering to a surface of acarbonaceous protective layer.

FIG. 3 shows a lubricant layer containing a host-guest complex accordingto the present invention in which the crown ether is used as a liquidlubricant.

FIG. 4 shows the chemical structure of cycloinulohexaose.

FIG. 5 shows adhesion of a host-guest complex to the surface of a solidsubstrate.

FIG. 6 shows an example of a host-guest complex composed of a long chainaliphatic amine as the guest lubricant molecule and an 18-crown-6derivative.

FIG. 7 is a graph showing layer thickness as a function of rinsing timesfor Example 14.

FIG. 8 is an analysis by FTIR-RAS of the orientation of the alkyl chainin the lubricant layer prepared in Example 2.

DETAILED EXPLANATION OF THE INVENTION

The present invention is described in detail below with reference to anexample in which the present invention is applied to the magneticrecording medium.

FIG. 1 shows a construction where the lubricant layer of the presentinvention is applied to the magnetic recording medium. In the magneticrecording medium comprising a non-magnetic substrate 1 on which amagnetic layer 2, a protective layer 3, and a lubricant layer 4 aresuccessively formed, the lubricant layer 4 comprises a host-guestcomplex in which a lubricant molecule is fixed as a guest moleculethrough a host compound adhering to the medium. In FIG. 1, theprotective layer 3 may be optionally arranged and the lubricant layer ofthe present invention may be directly formed on the surface of themagnetic layer 2.

A multidentate ligand having a polar functional group suitable forforming a hydrogen bond relating to a hydroxyl group, an amino group,and the like can be fixed on the surface of the medium through theelectrostatic interaction. It is possible to prevent the lubricantmolecules from cohering with each other when the lubricant layer isconstituted in such a manner that the lubricant molecule is coordinatedwith the multidentate ligand adhering to the surface of the medium. Tocoordinate the lubricant molecule with the multidentate ligand adheringonto the surface of the medium means that all of the long chainmolecular moieties are oriented upward against the surface of themedium, in principle. As a result, the orientation of the entirelubricant layer is improved to form an ideal structure for the lubricantlayer, which provides an excellent lubricating performance anddurability, notwithstanding the fact that the thickness of the lubricantlayer corresponds to that of a mono layer.

When the lubricant layer according to the present invention is appliedto the magnetic recording media, it is usually common to employ as thenon-magnetic substrate an aluminum alloy plate or a glass plate having anickel-phosphorus layer formed by electroless plating or sputtering. Aceramic substrate, a carbonaceous substrate, or a resin substrate canalso be used. It is recommended to adjust the average roughness of thesurface of the substrate to 20 to 100 Å, preferably 30 to 80 Å, bytexturing it in order to reduce the possible contact area with the headand bring out a more excellent tribology performance.

The magnetic layer is formed by coating a Co or Co-containing alloy suchas a CoP alloy, a CoNiP alloy, a CoNiCr alloy, a CoNiPt alloy, a CoCrPtalloy, a CoCrTa alloy, or a CoCrPtTa alloy by electroless plating orsputtering, after a undercoating layer is formed, if necessary. Thethickness of the magnetic layer is determined depending on theproperties required as the magnetic recording medium and usually rangesfrom 100 to 1,500 Å, preferably from 150 to 800 Å. When the lubricantlayer of the present invention is applied, the protective layer on thethin magnetic layer is not necessarily required and may be formed ifnecessary taking into account the physical properties such as thehardness or elasticity of the magnetic layer. A carbonaceous layer, anoxide layer, a nitride layer, or a boride layer is employed as theprotective layer. It can be formed by sputtering, ion plating, or plasmapolymerization. A carbonaceous layer such as amorphous carbon orhydrogenated carbon with the thickness of usually from 50 to 500 Å, andpreferably from 100 to 300 Å is usually used as the protective layer. Ifnecessary, the protective layer may be subjected to a surface treatmentsuch as oxidation.

When a carbonaceous layer is formed as the protective layer, the numberof acidic functional groups on the surface of the carbonaceousprotective layer can be increased by, for example, a wet treatment suchas a method comprising immersing the layer in a solution containing anoxidant and a dry treatment such as a method comprising irradiating thelayer with ultraviolet rays in an atmosphere of an oxygen-containinggas. The dry treatment is preferable from the industrial viewpoint. Aspecific example of the dry treatment includes a method comprisingirradiating the carbonaceous protective layer with ultraviolet rayshaving a wavelength of from 185 to 254 nm and an output of 50 W or moreat a distance of from 10 to 50 mm for 30 seconds to 15 minutes,preferably 1 to 5 minutes. An increase in the number of acidicfunctional groups on the surface of the carbonaceous protective layercan be confirmed by the quantitative determination of oxygen atom on thesurface and the ratio of the C═O bond to the C--C bond and the C--H bondthrough X-ray photoelectric spectrometry (hereinafter referred to asXPS). The XPS analysis can be carried out using AlK.sub.α rays at anoutlet angle of 65° (analysis depth up to 50 Å). According to thepresent invention, the ratio of the C═O bond to the C--C bond and theC--H bond is required to be 0.05 or more, preferably ranging from 0.05to 0.3, and more preferably within the range of from 0.07 to 0.2.

FIG. 2 shows the diagram of an 18-crown-6 derivative and potassiumstearate forming a host-guest complex and the complex adhering to thesurface of the carbonaceous protective layer of the medium. K⁺, which isa cation in the guest compound, is trapped in the internal cavity of thecrown ether, and stearate, which is a counter anion of K⁺, iscoordinated on the crown ether in such a manner that its terminalcarboxyl group as an ionic pair is oriented toward the trapped K⁺.Therefore, since the host compound, crown ether, adheres by binding toan acidic functional group 5 on the surface of the carbonaceousprotective layer 7 at the binding site 6 and an alkyl chain moiety ofthe guest compound, potassium stearate, that is, a stearyl group, isoriented upward against the substrate, the orientation of the wholelubricant layer is improved to form an ideal structure for a lubricantlayer, which provides an excellent lubricating performance anddurability, notwithstanding the fact that the thickness of the lubricantlayer corresponds to that of a mono layer. Further, the cohesion of thelubricant is suppressed by adhesion.

In the host-guest complex constituting the lubricant layer of thepresent invention, a usable guest molecule is one having a molecularstructure bearing a lubricating function and a binding site for bindingto a host molecule. Both the liquid lubricant structure and the solidlubricant structure can be employed as the molecular structure bearing alubricating function. An alkyl fluoride liquid lubricant such asperfluoropolyether, polybutene, polyalkylene glycol, phosphate,polyolefin, polyol ester, alkylnaphthalene, silicone oil,polyarylalkane, polyphenyl, silicate, or polyphenyl ether can be used asthe liquid lubricant structure. Examples of the perfluoropolyetherliquid lubricant include a Fomblin lubricant: --(CF₂ CF₂ O)_(m) (CF₂O)_(n) -- structure (manufactured by Mount Edison), a DEMNUM lubricant:--(CF₂ CF₂ CF₂ O)_(p) -- structure (manufactured by DAIKIN INDOSTRIESLTD.) and a KRYTOX lubricant: --(CF₂ CF(CF₃)O)_(q) -- structure(manufactured by DuPont) (m, n, p, or q is an integer of not less than1). The lubricant in which m, n, p, or q is 5 to 50 is usually used. Itsmolecular weight is preferably not less than 500, and particularlyranges from 600 to 8,000. A branched or straight, saturated orunsaturated, higher aliphatic hydrocarbon chain, a higher aliphatichydrocarbon chain containing an aromatic group, or a heteroatom or along chain structure in which a part or all of the above-describedhigher aliphatic hydrocarbon chain forms a polyether chain may be boundto the perfluoropolyether molecular structure. FIG. 3 shows the diagramof the lubricant layer containing the host-guest complex according tothe present invention in which the crown ether is used as the liquidlubricant.

The solid lubricant can take any structure such as a branched orstraight, saturated or unsaturated, higher aliphatic hydrocarbon chain,the above-described higher aliphatic hydrocarbon chain containing anaromatic residue such as benzene, naphthalene, or pyrene or a heteroatomsuch as F, N, O or S, or a long chain in which a part or all of theabove-described higher aliphatic hydrocarbon chain forms a polyetherchain. Any structure can be used independent of the nature of bond aslong as it has a lubricating function. The carbon number contained inthe long chain is preferably 8 or more, and more preferably 12 or more.Since its solubility in a solvent may become poor when the chain lengthof a straight chain alkyl group is too long, the simple straight chainalkyl group (i.e., comprising carbon-carbon bonds such as continuousmethylene-methylene bonds) preferably has 24 or fewer carbon atoms.Specific examples thereof include long chain aliphatic carboxylic acidssuch as stearic acid, compounds containing plural long chain alkylgroups such as β-(N,N-diheptadecylaminocarbonyl)propionic acid,phosphoric acid esters of long chain aliphatic compounds such as dioleylphosphate, dithiophosphoric acid ester of long chain aliphaticcompounds, long chain aliphatic sulfonic acids, sulfuric acid esters oflong chain aliphatic compounds, and long chain aliphatic alcohols suchas stearyl alcohol.

The binding site for binding the lubricant compound to the host compoundis selected so that the binding site can be trapped in the cavity of thehost compound. Alkaline metals such as Na, K, or Rb, alkaline earthmetals such as Mg, Cs, Sr, or Ba, typical metals such as Al, Sn, or Pb,or transition metals such as Ag, Cu, or Fe are usually used for bindingto the terminal group of the molecular structure bearing the lubricatingfunction. Specific examples of the terminal group include anoxygen-containing polar functional group such as a hydroxyl group, acarboxyl group, an ester bond, or an amide bond, a nitrogen-containingfunctional group such as an amino group or an imino group, aphosphorus-containing functional group such as phosphoric acid orphosphoric acid ester and a sulfur-containing functional group such as amercapto group, a sulfonic acid group, or sulfonic acid ester. Theseterminal groups or the lubricants having an ammonium salt or an amineacid salt at the terminal can also be used alone, without combining themwith metal ions as an organic ion. In this case, the terminal functionalgroup of the lubricant molecule is trapped in the cavity of the hostmolecule. K, Ba, Ag, Cu, an amino group, an ammonium salt or a hydroxylgroup is particularly preferred as the binding site. The surface of thecarbonaceous protective layer having an acidic functional group can beeffectively fixed by using as the host compound the multidentate ligandto which the basic functional group such as amino group or imino grouphas been introduced.

A multidentate ligand capable of effectively trapping a metal ion or anorganic ion, including cyclic esters, polyethers, polyols, polyamines,cyclic ethers called crown ether or cyclofructans, cyclic ether aminescalled cryptand or cryptate, cyclic amines, polypeptides, and theirchemically modified forms can be used as the host molecule. Themultidentate ligand having terminal functional groups bearing theelectrostatic interaction can also be used as the host molecule. Cyclicligands such as crown ether or cryptand are particularly useful.Examples of the cyclofructans include those containing 18-crown-6 as abasic structure such as cycloinulohexaose and analogs thereof, thosecontaining 4,4'-dihydroxydibenzo-18-crown-6 or 21-crown-7 as the basicstructure such as cycloinuloheptaose and those containing 24-crown-8 asthe basic structure such as cycloinulooctaose. Cycloinulohexaose or4,4'-dihydroxydibenzo-18-crown-6 is particularly preferably used. Acyclic amine such as 1,4,8,11-tetraazacyclotetradecane orN,N'-dibenzyl-4,13-diaza-18-crown-6 can also be used. A compoundcontaining three or more donor atoms of at least one element such as O,N, or S is suitably used as the multidentate ligand. The donor atoms ofthe multidentate ligand preferably contains a lone electron pair havingan sp³ hybrid orbital.

FIG. 4 shows the structure of cycloinulohexaose among the cyclofructansformed by binding a fructose molecule via a β-(2→1) bond, as an exampleof the multidentate ligand used in the magnetic recording mediumaccording to the present invention. The multidentate ligand is requiredto have two or more functional groups, and preferably four or morefunctional groups, per molecule, bearing an electrostatic interactionsuch as a hydroxyl group as well as a cyclic ligand portion trapping ametal ion, like cyclofructans as shown.

The multidentate ligand forms a strong complex with a metal ion or anorganic ion. For example, since the lone electron pair such as O or Ncontained in the cyclic ligand such as crown ether or cryptand islocated in the internal cavity of the ligand and shows high affinity fora metal ion and the like, the equilibrium of the complex formationusually inclines toward the side of the complex formation within a rangeof from 10² to 10¹⁰ to trap the metal ion very strongly. Namely, in thecyclic ligand, O or N is coordinated as a donor atom by theelectrostatic interaction with the lone electron pair as the maindriving force, and a metal cation is effectively trapped in the internalcavity of the ligand. Compared to a monodentate ligand, these cyclicligands have great advantages in that no new repulsion between donorsoccurs when they are coordinated around the cation since the donor atomsuch as O or N is originally linked via a methylene bridge, which isadvantageous to the complex formation in terms of enthalpy, and alsohave advantage in view of entropy because of the suitable placement ofthe donor atoms. A straight chain multidentate ligand is useful as wellas the cyclic multidentate ligand, but it has been found that thestability of the complex increases in the case of using the cyclicligand as compared to the straight chain ligand. This may be attributedto the electrostatic and stearic repulsion between the donor atoms atboth ends and the disadvantageous change of entropy though the straightchain multidentate ligand is superior to the monodentate ligand intrapping of a cation. There are several reviews on the above-mentionedcyclic ligands. For example, J. J. Christensen et al. describe adetailed table reciting the synthetic methods, structure, and cation tobe trapped concerning typical ligands, crown ether, cryptand, and theiranalogs, in Chem. Revs., 74, 351 (1974). From the viewpoint of stabilityas a substance, many cyclic multidentate ligands are thermally stable.It has been reported, for example, that dibenzo-18-crown-6 can bedistilled at 380° C. (C. J. Pederson et al., Angev. Chem., Int'L, Ed.11, 16 (1972)).

It has been found that there is a close relationship between the size ofthe internal cavity of the cyclic ligand and the size of the cation tobe easily trapped upon the complex formation. For example, 18-crown-6having an internal cavity diameter of from 2.6 to 3.2 Å has been knownto form a very stable complex with alkaline metal K⁺ having an iondiameter (2.66 Å) which is almost in conformity with the internaldiameter (complexing equilibrium constant in methanol logK=6.05).

Thus, on the one hand, the lubricant molecule (guest molecule) can befixed onto the substrate through an electrostatic interaction by forminga complex composed of the lubricant molecule and the multidentate ligand(host compound) adhering onto the solid substrate as a specificallystable host-guest complex. FIG. 5 shows the diagram of the manner ofadhesion of the host-guest complex composed of 18-crown-6 derivative andpotassium stearate to the surface of the solid substrate. K⁺, which is acation in the guest molecule, is trapped in the internal cavity of thecrown ether and stearate, which is a counter anion of K⁺, is coordinatedon the crown ether in such a manner that its terminal carboxyl group asan ionic pair is oriented toward the trapped K⁺. On the other hand, thehost molecule, crown ether, can be fixed onto the disk surface by, forexample, adequate chemical modification. Hence, the terminal carboxylgroup of the lubricant moiety (a long chain alkyl stearate group) isfixed onto the crown ether complex on the substrate surface, whichprevents the lubricant molecules from cohering with each other. Tocoordinate the terminal carboxyl group to the crown ether complex on thesubstrate means that all of the alkyl chain are oriented upward againstthe substrate in principle. As a result, the orientation of the entirelubricant layer is improved to form an ideal structure of the lubricantlayer, which provides an excellent lubricating performance anddurability, notwithstanding the fact that the thickness of the lubricantlayer corresponds to that of a mono layer.

Similarly, the lubricant having excellent properties can be obtained byforming the host-guest complex through electrostatic interaction usingan organic compound having a polar functional group such as amino groupand the multidentate ligand. An example is the host-guest complexcomposed of long chain aliphatic amine as the guest lubricant moleculeand the 18-crown-6 derivative shown in FIG. 6. In this case, the bindingsite which interacts with the multidentate ligand is located on theligand and the complex is formed in such a manner that the lubricantmoiety is arranged on the multidentate ligand, such as in the case ofusing potassium stearate as the guest compound.

The lubricant layer containing the host-guest complex can be formed onthe solid substrate by mixing the multidentate ligand used as the hostcompound with the lubricant molecule used as the guest compound andcoating the resulting mixed solution in which the host-guest complex isformed on the disk. The multidentate ligand is adsorbed by or adheres tothe surface of the solid substrate through interaction with the solidsurface by using the mixed solution to form a layer structure in whichthe lubricant molecule is coordinated on the solid surface.

The lubricant layer can be formed by coating a host-guest complexcomposed of a multidentate ligand (a host compound) having a function totrap a metal ion or an organic ion and a lubricant molecule (a guestcompound) comprising an organic ion to which a molecular structurebearing a lubricating function is bound or a metal ion to which acounter anion bearing a lubricating function is bound.

Alternatively, the host-guest complex lubricant layer can be formed by amethod comprising forming of the multidentate ligand layer to serve asthe host compound on the surface of the substrate and then forming thelubricant molecule layer to serve as the guest compound to form thehost-guest complex with the host compound. According to this method,since the multidentate ligand layer is certainly adsorbed by or adheresto the solid surface and can then form the host-guest complex with thelubricant molecule, an elaborate lubricant layer can be formed morereliably when not only the lubricant molecule having a very highmolecular weight but also the lubricant molecule having a comparativelylow molecular weight is used as the guest molecule. The latter method ispreferred to the method of using a mixed solution of the host-guestcomplex in cases where it is difficult to fix the host compound onto thesolid surface elaborately, for example, in the case where the lubricantchain is very long and steric hindrance cannot be ignored.

It is possible to form the multidentate ligand layer on the solidsurface and then form the lubricant molecule layer on the multidentateligand layer. If the multidentate ligand layer is unnecessarily thick,the surplus part of the multidentate ligand may be removed, leaving onlya layer adsorbed or fixed onto the solid surface, and then the lubricantmolecule layer is formed. As a result, the thickness of the entirelubricant layer can be made thin to enhance the adherence between thelubricant molecule and the solid surface via the multidentate ligandlayer.

The surplus part of the multidentate ligand layer can usually be removedby a method comprising rinsing with a solvent capable of dissolving themultidentate ligand or a method comprising a physical treatment.Examples of the rinsing method include a method comprising immersing thedisk on which the multidentate ligand layer is formed in the solvent andthen raising it to wash the disk surface with the solvent. Even thoughthe solvent is required to have the ability to dissolve the multidentateligand, the use of a solvent so strong that it completely elutes themultidentate ligand layer adsorbed or fixed onto the solid surface is tobe avoided, however. It is preferable from the industrial viewpoint touse the same solvent as the one to be used for the lubricant solution inthe subsequent step of forming the lubricant layer because the lubricantsolution then cannot be contaminated with the multidentate ligand uponthe formation of the lubricant layer.

In the case that the host-guest complex lubricant layer is formed so asto have a structure such that the counter anion having a lubricatingperformance is fixed through the metal ion trapped by the multidentateligand, that is, the host compound, having a function to trap the metalion, the method of forming the lubricant layer includes, a methodcomprising preparing a solution in which a metal salt of the lubricantmolecule and the multidentate ligand are dissolved or dispersed or asolution in which the lubricant molecule, a metal compound, and themultidentate ligand are dissolved or dispersed, and coating this mixedsolution on the substrate surface and a method comprising forming amultidentate ligand-adhering layer on the substrate surface and thenforming the lubricant molecule layer on the multidentate ligand layerusing a solution containing the lubricant molecule.

In the method comprising forming a multidentate ligand-adhering layer onthe substrate surface and then forming the lubricant molecule layer onthe multidentate ligand layer using a solution containing the lubricantmolecule, a solution containing the lubricant molecule and the metalcompound or a metal salt of the lubricant molecule may be coated on thesubstrate surface after a solution of the multidentate ligand is coatedthereon. Alternatively, the lubricant molecule-containing solution maybe coated on the substrate surface after the multidentate ligandsolution in which the metal compound is mixed is coated thereon.According to this method, since it is possible to form the multidentateligand layer on the substrate and thereafter form the host-guest complexwith the lubricant molecule, the desired host-guest complex can bereliably constructed not only when the molecular weight of the lubricantmolecule is comparatively low but also when the molecular weight ishigh, such as is the case with a polymer.

A case may arise in which the isolation and purification step of theguest compound to prepare the metal salt requires a large amount ofsolvent and prolonged time. In this instance, using a solution in whicha multidentate ligand having the function to trap a metal ion, a metalcompound, and a lubricant molecule having active hydrogen are dissolvedor dispersed, where the lubricant molecule has a functional groupcapable of forming an ionic pair with the metal ion, like a carboxylgroup, at its terminal, a compound difficult to be isolated and purifiedin the form of a metal salt, or a compound which cannot be isolated andpurified can be employed as the lubricant molecule to be used for thehost-guest complex lubricant layer. To omit the isolation andpurification step is industrially advantageous in obtaining thelubricant layer which is more widely usable.

Any metal compound can be employed as long as its metal ion can besubjected to cation-exchange with active hydrogen (proton) at theterminal of the above lubricant molecule. The metal compound ispreferably soluble in water or an organic solvent. Examples thereofinclude a salt such as alcoholate, phenolate, and the like, with analkaline metal compound including a hydroxide such as potassiumhydroxide and the like being preferred.

The multidentate ligand having the function to trap a metal ion, themetal compound, and the lubricant molecule having active hydrogen aredissolved in a solvent independently or in an appropriate combinationand the thus-obtained solution can be coated on the solid surface. Forexample, in a system using 4,4'-diaminodibenzo-18-crown-6 as themultidentate ligand, potassium hydroxide as the metal compound, andstearic acid as the lubricant molecule, stearic acid and4,4'-diaminodibenzo-18-crown-6 are dissolved in chloroform or methanol,potassium hydroxide is dissolved in methanol or water, and a mixedsolution of 4,4'-diaminodibenzo-18-crown-6, potassium hydroxide, andstearic acid can be prepared by using these solutions. In a case wherethe three are independently dissolved or two of them are combined,dissolved in a solvent, and coated on the solid substrate, it ispreferable to coat the solution containing the multidentate ligand firston the solid surface. An elaborate lubricant layer can be prepared morereliably even when the lubricant molecule has as high a molecular weightas a polymer or when it has a comparatively low molecular weight. Thelubricant layer formed by coating the multidentate ligand having thefunction to trap the metal ion, the metal compound, and the lubricantmolecule having active hydrogen independently as a material on the solidsubstrate shows the same ability as the lubricant layer formed using theguest compound which has been isolated and purified as a metal salt.

As the method of forming the lubricant layer, each compound can also beaffixed to the solid substrate by a dry process such as vapordeposition. In this case, the multidentate ligand, the metal compound,and the lubricant molecule may be adhered simultaneously orsuccessively. In the case of successive adherence, the metal compoundcan be introduced into the step of affixing the multidentate ligand orthe lubricant molecule to form the lubricant layer in two steps.

The host-guest complex composed of the above-described host and guestcompounds may be obtained in the form of a solution or a dispersion bydissolving or dispersing the host compound and the guest compound in asolvent. It may be obtained by mixing their solutions or dispersionswhich have been prepared in advance. One of the main characteristics ofthe host-guest complex is that, if a guest compound is insoluble in anorganic solvent like a metal salt, the complex formed with such a guestcompound and a host compound soluble in an organic solvent may dissolvein a commonly employed organic solvent. For example, a metal salt of ahigher fatty acid such as potassium stearate, which is a typicallubricant, is hardly dissolved in an organic solvent such as chloroform,while a host-guest complex composed of it and 18-crown-6, which is atypical host compound, dissolves well in an organic solvent. This isbecause the crown ether solubilizes potassium stearate by trapping apotassium ion therein. An organic solvent or water can be used as asolvent in the formation of the host-guest complex. Examples of theorganic solvent are commonly employed organic solvents having acomparatively low boiling point, for example, including halogenatedhydrocarbons such as chloroform, fluorocarbon solvents, alcohols such asmethanol or ethanol, ethers such as diethyl ether, tetrahydrofuran,ketones such as acetone or 2-hexanone, aromatic hydrocarbons such astoluene, aliphatic hydrocarbons such as hexane, and esters such as ethylacetate, which may be used alone or as a mixed solvent.

The thus-obtained solution or dispersion of the host-guest complex canbe coated on the solid surface as a lubricant as is or after adjustingits concentration.

The lubricant containing the host-guest complex can usually be coated onthe surface of the solid substrate by immersing the solid substrate inthe solution. It may also be coated by a method comprising bringing atape or the like impregnated with the solution into contact with thesurface of the solid substrate with a load to form a coated layer, amethod comprising affixing it by rotating a pad on the solid substrate,or a spray coating method, the LB method, and the like. Theconcentration of the coating solution varies depending on the solutes orsolvents to be used, but it usually ranges from 0.1 to 5 g/l in terms ofa total solute. The thickness of the lubricant layer varies depending onthe host compound and the guest compound to be used, but it usuallyranges from 10 to 100 Å, preferably 10 to 50 Å.

EXAMPLES

The following Examples will be provided to illustrate the presentinvention in detail, but should not be understood to limit the presentinvention unless it goes beyond the scope of the invention.

Example 1

A chromium undercoating layer (2,000 Å), a magnetic layer of a cobaltalloy (400 Å), and a carbonaceous protective layer (300 Å) were formedin order on an aluminum alloy substrate by sputtering to obtain amagnetic disk having a diameter of 3.5 inches. The resulting disk wasimmersed in a chloroform solution containing potassium stearate and4,4'-diaminodibenzo-18-crown-6, each in a concentration of 1 mmol/l(0.713 g/l in total) for 5 minutes and was raised at a rate of 10 mm/sto form an even lubricant layer having a thickness of 29 Å on the disksurface.

4,4'-Diaminodibenzo-18-crown-6 was obtained in the isolation yield of90% by reducing 4,4'-dinitrodibenzo-18-crown-6 with hydrazine byreference to the method of E. Shchori et al. (J. Am. Chem. Soc., 95,3842 (1973)). 4,4'-Dinitrodibenzo-18-crown-6 was obtained in theisolation yield of 81% by the nitration of a commercially availabledibenzo-18-crown-6 by reference to the method of W. M. Freigenbaum etal. (J. Polym. Sci., Part A-1, 9, 817 (1971)).

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test. The lubricatingperformance test was carried out by continuously sliding the disk by theuse of a thin film head slider under conditions of a load of 9.5 gf anda sliding linear rate of 0.32 m/s (30-mm radius, 100 rpm) and measuringthe friction force after 2 hours of continuous sliding. The cohesiontest was carried out by allowing the disk to stand in the atmosphere ata constant temperature and a constant humidity and observing thecohesion or crystallization under an optical microscope. The results areshown in Table 2.

Example 2

The same disk as used in Example 1 was immersed in a chloroformcontaining potassium β-(N,N-diheptadecyl-aminocarbonyl)propionate and4,4'-diaminodibenzo-18-crown-6, each in a concentration of 1 mmol/l(1.02 g/l in total) for 5 minutes and was raised at a rate of 10 mm/s toform an even lubricant layer having a thickness of 45 Å on the disksurface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. In the lubricating performance test, the friction forcewas measured after 10 minutes and after 2 hours of continuous sliding.The results are shown in Table 2.

Example 3

A chromium undercoating layer (1,200 Å), a magnetic layer of a cobaltalloy (500 Å), and a hydrogenated carbonaceous protective layer (200 Å)were formed in order on a smooth aluminum alloy substrate having anaverage central line roughness (Ra) of 35 Å, by sputtering to obtain amagnetic disk having a diameter of 3.5 inches. The disk was irradiatedwith ultraviolet rays having a wavelength of 185 nm and 254 nm and anoutput of 90 W from a distance of 15 mm for 5 minutes in the air,followed by dipping in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6-ether in a concentration of 2 mmol/l(0.781 g/l) to form an even layer having a thickness of 15 Å on the disksurface.

The resulting disk was then immersed in a chloroform for 5 minutes andwas raised to leave an even layer having a thickness of 5 Å on the disksurface.

An even layer having a thickness of 25 Å was formed on the disk surfaceby dipping in a solution of DEMNUM SH (one-end COOH-denatured product;average molecular weight: 1,650; manufactured by DAIKIN INDUSTRIES,LTD.) and potassium hydroxide dissolved in a fluorine solvent PF5080 (asolution manufactured by SUMITOMO 3M LIMITED), each in a concentrationof 0.33 mol/l.

The disk on which the lubricant layer was formed was subjected to alubricant spin-off test and a contact start and stop test (CSS test).The results are shown in Table 1. The spin-off test was carried out byrotating the disk in an atmosphere of 80° C. for 14 days at 7,200 rpmand determining the percentages of the residual thickness of thelubricant layer from the change in the absorption intensity of C--F bondin the FTIR spectrum.

The CSS test was carried out using a 70% thin film head slider(material: Al₂ O₃. TiC; a pressing load: 6 gf) which was raised to 75 nmat a peripheral speed of 8.7 m/s. One CSS cycle took 12 seconds,consisting 3 seconds for turning on the electricity to a spindle and 9seconds for switching the electricity source off. The torque at the timeof the initiation of spindle rotation and the torque during sliding weremeasured in each cycle. The torque during sliding was calculated from amaximum power acting on the head between 0.3 second and 1 second afterturning on the electricity to the spindle. 20,000 CSS cycles wereconducted and the average values of the torque at the time of theinitiation of the rotation and the torque during sliding were calculatedfrom the ten highest values. No stain was observed on either the disk orthe head after the CSS test.

Example 4

The same disk as used in Example 3 was subjected to ultraviolet raysirradiation and an even layer having a thickness of 18 Å was formed onthe disk surface by dipping in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l (0.781g/l).

The resulting disk was then immersed in a chloroform for 5 minutes andwas raised to leave an even layer having a thickness of 9 Å on the disksurface.

An even layer having a thickness of 26 Å (Example 4-1, for a spindletest) or 24 Å (Example 4-2, for a CSS test) was formed on the disksurface by dipping in a PF5080 solution containing DEMNUM SH (averagemolecular weight: 2,400) and potassium hydroxide, each in aconcentration of 0.4 mmol/l).

The disk on which the lubricant layer was formed was subjected to aspindle test or a CSS test in the same manner as in Example 3. Theresults are shown in Table 1. No stain was observed on either the diskor the head after the CSS test.

Example 5

The same disk as used in Example 3 was subjected to ultraviolet raysirradiation and an even layer having a thickness of 16 Å was formed onthe disk surface by dipping in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l (0.781g/l).

The resulting disk was then immersed in a chloroform for 5 minutes andwas raised to leave an even layer having a thickness of 8 Å on the disksurface.

An even layer having a thickness of 44 Å was formed on the disk surfaceby dipping in a PF5080 solution containing DEMNUM SH (average molecularweight: 2,400) and potassium hydroxide, each in a concentration of 0.6mmol/l.

The disk on which the lubricant layer was formed was subjected to aspin-off test in the same manner as in Example 3. The results are shownin Table 1.

Example 6

The same disk as used in Example 3 was subjected to ultraviolet raysirradiation and an even layer having a thickness of 15 Å was formed onthe disk surface by dipping in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l (0.781g/l).

The resulting disk was then immersed in a chloroform for 5 minutes andwas raised to leave an even layer having a thickness of 6 Å on the disksurface.

An even layer having a thickness of 18 Å was formed on the disk surfaceby dipping in a PF5080 solution containing perfluoropolyether Fomblin ZDOL (OHs at both ends; average molecular weight: 2,000; manufactured byMount Edison) in a concentration of 1 g/l.

The disk on which the lubricant layer was formed was subjected to aspin-off test in the same manner as in Example 3. The results are shownin Table 1.

Comparative Example 1

The same disk as used in Example 1 was immersed in a methanol solutioncontaining potassium stearate in a concentration of 1 mmol/l (0.316 g/l)for 5 minutes and was raised at a rate of 10 mm/s to form a lubricantlayer having a thickness of 13 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. In the lubricating performance test, the friction forcewas measured after 10 minutes and after 2 hours of continuous sliding.The results are shown in Tables 2 and 3.

Comparative Example 2

The same disk as used in Example 1 was immersed in a chloroformcontaining stearic acid in a concentration of 3 mmol/l (0.852 g/l) for 5minutes and was raised at a rate of 10 mm/s to form a lubricant layerhaving a thickness of 16 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. The results are shown in Table 2.

Comparative Example 3

The same disk as used in Example 1 was immersed in a chloroformcontaining β-(N,N-diheptadecylaminocarbonyl)-propionic acid in aconcentration of 1 mmol/l (0.593 g/l) for 5 minutes and was raised at arate of 10 mm/s to form an even lubricant layer having a thickness of 28Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. In the lubricating performance test, the friction forcewas measured after 10 minutes and after 2 hours of continuous sliding.The results are shown in Table 2.

Comparative Example 4

A hydrogenated carbonaceous protective layer was formed on the same diskas used in Example 3 and an even layer having a thickness of 20 Å wasformed on the disk surface by dipping in a PF5080 solution containingDEMNUM SH (average molecular weight: 1,650) in a concentration of 0.5mmol/l.

The disk on which the lubricant layer was formed was subjected to aspin-off test in the same manner as in Example 3. The results are shownin Table 1.

Comparative Example 5

A hydrogenated carbonaceous protective layer was formed on the same diskas used in Example 3 and an even layer having a thickness of 31 Å(Comparative Example 5-1, for a spindle test) or 27 Å (ComparativeExample 5-2, for a CSS test) was formed on the disk surface by dippingin a PF5080 solution containing DEMNUM SH (average molecular weight:2,400) in a concentration of 0.6 mmol/l.

The disk on which the lubricant layer was formed was subjected to aspindle test or a CSS test in the same manner as in Example 3. Theresults are shown in Table 1. No stain was observed on either the diskor the head after the CSS test.

Comparative Example 6

A hydrogenated carbonaceous protective layer was formed on the same diskas used in Example 3 and an even layer having a thickness of 41 Å wasformed on the disk surface by dipping in a PF5080 solution containingDEMNUM SH (average molecular weight: 2,400) in a concentration of 0.6mmol/l.

The disk on which the lubricant layer was formed was subjected to aspin-off test in the same manner as in Example 3. The results are shownin Table 1.

Comparative Example 7

A hydrogenated carbonaceous protective layer was formed on the same diskas used in Example 3 and an even layer having a thickness of 21 Å(Comparative Example 7-1, for a spindle test) or 16 Å (ComparativeExample 7-2, for a CSS test) was formed on the disk surface by dippingin a PF5080 solution containing perfluoropolyether Fomblin Z DOL(average molecular weight: 2,000) in a concentration of 1 g/l.

The disk on which the lubricant layer was formed was subjected to aspindle test or a CSS test in the same manner as in Example 3. Theresults are shown in Table 1. No stain was observed on either the diskor the head after the CSS test.

Example 7

The same disk as used in Example 1 was dipped in a mixture of chloroformand methanol containing 4,4'-diaminodibenzo-18-crown-6, potassiumhydroxide and stearic acid, each in a concentration of 1 mmol/l to forman even lubricant layer having a thickness of 21 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the atmosphere at atemperature of 25° C. and a humidity of 40% RH in the same manner as inExample 1. The results are shown in Table 2.

Example 8

The same disk as used in Example 1 was dipped in a mixture of chloroformand methanol containing 4,4'-diaminodibenzo-18-crown-6, potassiumhydroxide and β-(N,N-diheptadecylaminocarbonyl)propionic acid, each in aconcentration of 1 mmol/l to form an even lubricant layer having athickness of 33 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 7. The results are shown in Table 2.

Example 9

The same disk as used in Example 1 was dipped in a chloroform solutioncontaining 4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/lto form an even layer having a thickness of 12 Å on the disk surface.The resulting disk was then immersed in a mixture of chloroform andmethanol containing β-(N,N-diheptadecylaminocarbonyl)propionic acid andpotassium hydroxide, each in a concentration of 1 mmol/l, and was raisedto form an even lubricant layer having a thickness of 33 Å on the disksurface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 7. The results are shown in Table 2.

Example 10

The same disk as used in Example 1 was dipped in a chloroform solutioncontaining 4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/lto form an even layer having a thickness of 14 Å on the disk surface.The resulting disk was immersed in a chloroform for 5 minutes and wasraised at a rate of 2 mm/s to leave an even layer having a thickness of8 Å on the disk surface. The disk was then immersed in a mixture ofchloroform and methanol containingβ-(N,N-diheptadecylaminocarbonyl)propionic acid and potassium hydroxide,each in a concentration of 1 mmol/l, and was raised to form an evenlubricant layer having a thickness of 26 Å.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 7. The results are shown in Table 2.

Example 11

The same disk as used in Example 1 was immersed in a mixture ofchloroform and methanol containing 4,4'-diaminodibenzo-18-crown-6 andstearic acid, each in a concentration of 1 mmol/l to form an evenlubricant layer having a thickness of 17 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 7. The results are shown in Table 3.

Example 12

The same disk as used in Example 1 was immersed in a mixture ofchloroform and methanol containing 4,4'-diaminodibenzo-18-crown-6 andβ-(N,N-diheptadecylaminocarbonyl)propionic acid, each in a concentrationof 1 mmol/l to form an even lubricant layer having a thickness of 31 Åon the disk surface.

The disk on which the lubricant layer was subjected to a lubricatingperformance test and a cohesion test in the same manner as in Example 7.The results are shown in Table 3.

Example 13

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining 4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l(0.781 g/l) and was raised to form an even layer having a thickness of14 Å on the disk surface.

The resulting disk was then immersed in a chloroform solution (1.26 g/l)containing potassium β-(N,N-diheptadecylaminocarbonyl)-propionate in aconcentration of 2 mmol/l and was raised to form an even lubricant layerhaving a thickness of 49 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the atmosphere at atemperature of 25° C. and a humidity of 40% RH in the same manner as inExample 1. The results are shown in Table 2.

Example 14

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining 4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l(0.781 g/l) and was raised to form an even layer having a thickness of16 Å on the disk surface. The resulting disk was immersed in achloroform solution for 5 minutes and was raised at a rate of 2 mm/s toleave an even fixed layer having a thickness of 7 Å on the disk surface.As shown in FIG. 7, this fixed layer was not removed after repeated(three times in total) rinsing with a chloroform solution in a similarmanner, which means that 4,4'-diaminodibenzo-18-crown-6 used as amultidentate ligand in this Example strongly adheres to the carbonaceousprotective layer.

The disk obtained through the above steps was immersed in a chloroformsolution containing potassiumβ-(N,N-diheptadecylaminocarbonyl)propionate in a concentration of 2mmol/l (1.26 g/l) and was raised to form an even lubricant layer havinga thickness of 28 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 13. The results are shown in Table 2.

Example 15

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining potassium stearate and 4,4'-diaminodibenzo-18-crown-6, eachin a concentration of 1 mmol/l and was raised to form an even lubricantlayer having a thickness of 17 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test in the same manner as in Example 1 tomeasure the friction force after 10 minutes and after 2 hours ofcontinuous sliding. The results are shown in Table 3.

Example 16

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining potassium stearate in a concentration of 1 mmol/l anddibenzo-18-crown-6 in a concentration of 2 mmol/l (1.03 g/l in total)and was raised to form an even lubricant layer having a thickness of 16Å on the disk surface.

This Example was carried out to confirm the lubricating performanceunder a condition in which the dibenzo-18-crown-6 was present in thesystem in a large excess when compared to potassium stearate, namely,the absence of free potassium stearate.

The disk on which the lubricant layer was formed was subjected to alubricating performance test in the same manner as in Example 15. Theresults are shown in Table 3.

Example 17

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining stearylamine and dibenzo-18-crown-6, each in a concentrationof 1 mmol/l (1.89 g/l in terms of a complex) and was raised to form aneven lubricant layer having a thickness of 24 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test in the same manner as in Example 15. Theresults are shown in Table 3.

Comparative Example 8

The same disk as used in Example 1 was immersed in a chloroform solutioncontaining stearylamine in a concentration of 3 mmol/l (0.809 g/l) andwas raised to form a lubricant layer having a thickness of 25 Å on thedisk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test in the same manner as in Example 14. Theresults are shown in Table 3.

Example 18

The same disk as used in Example 1 was immersed in a methanol solutioncontaining cycloinulohexaose and potassiumβ-(N,N-diheptadecylaminocarbonyl)propionate were dissolved, each in aconcentration of 1 mmol/l and was raised to form an even lubricant layerhaving a thickness of 23 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the atmosphere at atemperature of 60° C. and a humidity of 80% RH. The results are shown inTable 4.

Example 19

The same disk as used in Example 1 was immersed in a methanol solutioncontaining cycloinulohexaose, β-(N,N-diheptadecylaminocarbonyl)propionicacid and potassium hydroxide were dissolved, each in a concentration of1 mmol/l and was raised to form an even lubricant layer having athickness of 30 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 18. The results are shown in Table 4.

Example 20

The same disk as used in Example 1 was immersed in a methanol solutioncontaining cycloinulohexaose in a concentration of 1 mmol/l and wasraised to form an even layer having a thickness of 16 Å on the disksurface. The resulting disk was then immersed in a chloroform solutioncontaining potassium β-(N,N-diheptadecylaminocarbonyl)propionate in aconcentration of 2 mmol/l and was raised to form an even lubricant layerhaving a thickness of 50 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 18. The results are shown in Table 4.

Comparative Example 9

The disk on which the lubricant layer was formed in the same manner asin Comparative Example 3 was subjected to a lubricating performance testand a cohesion test in the same manner as in Example 18. The results areshown in Table 4.

Example 21

On a smooth aluminum alloy substrate having a diameter of 3.5 inches,1,200 Å of a chromium undercoating layer and 500 Å of a magnetic layerof a cobalt alloy were formed by sputtering. 200 Å of a hydrogenatedcarbonaceous protective layer was further formed on the disk. Thesurface of the resulting disk was irradiated with ultraviolet rayshaving a wavelength of 185 nm and 254 nm and an output of 90 W from adistance of 15 mm for 5 minutes in the air.

The surface of the hydrogenated carbonaceous protective layer wasanalyzed by XPS using an A1Kα rays, 14 kv-300 W, monochromator as anX-ray source, for an analysis area of 0.8×3.5 mm and an outlet angle of65° (analysis depth: up to -50 Å). As a result, oxygen was contained in20 atm %. The ratio of the C═O bond to the C--H bond and C--C bondchanged from 0.04 before the surface treatment to 0.10 after the surfacetreatment. This means that the acidic functional groups on the surfaceof the hydrogenated carbonaceous protective layer had increased.

The resulting disk was immersed in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l (0.781g/l) to form an even layer having a thickness of 20 Å on the disksurface. This disk was then immersed in a chloroform for 5 minutes andwas raised at a rate of 2 mm/s to leave an even layer having a thicknessof 12 Å on the disk surface.

The disk was then immersed in a methanol solution containing potassiumstearate in a concentration of 1 mmol/l (0.314 g/l) and was raised toform an even lubricant layer having a thickness of 19 Å.

The disk on which the lubricant layer was formed was subjected to a CSStest in the same manner as in Example 3 and a cohesion test in theatmosphere at a temperature of 25° C. and a humidity of 40% RH in thesame manner as in Example 1. The results are shown in Table 5.

Example 22

The same disk as used in Example 21 was subjected to ultraviolet raysirradiation and was immersed in a chloroform solution containing4,4'-diaminodibenzo-18-crown-6 in a concentration of 2 mmol/l (0.781g/l) to form an even layer having a thickness of 17 Å on the disksurface.

The resulting disk was immersed in a chloroform for 5 minutes and wasraised at a rate of 2 mm/s to leave an even layer having a thickness of12 Å on the disk surface.

The disk was then immersed in a chloroform solution containing potassiumβ-(N,N-diheptadecylaminocarbonyl)propionate in a concentration of 2mmol/l (1.26 g/l) and raised to form an even lubricant layer having athickness of 38 Å.

The disk on which the lubricant layer was formed was subjected to a CSStest and a cohesion test in the same manner as in Example 21. Theresults are shown in Table 5.

Example 23

The same disk as used in Example 1 was subjected to ultraviolet raysirradiation and was immersed in a chloroform solution containingpotassium stearate and dibenzo-18-crown-6, each in a concentration of 1mmol/l (0.674 g/l in total) to form an even lubricant layer having athickness of 26 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to a CSStest and a cohesion test in the same manner as in Example 21. Theresults are shown in Table 5.

Example 24

The same disk as used in Example 1 was subjected to ultraviolet raysirradiation and was immersed in a chloroform solution containingpotassium β-(N,N-diheptadecylaminocarbonyl)propionate and4,4'-diaminodibenzo-18-crown-6, each in a concentration of 1 mmol/l(1.02 g/l) to form an even lubricant layer having a thickness of 36 Å onthe disk surface.

The disk on which the lubricant layer was formed was subjected to a CSStest and a cohesion in the same manner as in Example 21. The results areshown in Table 5.

Comparative Example 10

Using the same disk as used in Example 21 but without irradiating itwith ultraviolet rays, an even lubricant layer having a thickness of 20Å was formed on the disk surface by immersing in a fluorocarbon solutioncontaining perfluoropolyether (Fomblin Z DOL, manufactured by MountEdison) in a concentration of 1 g/l.

The disk on which the lubricant layer was formed was subjected to a CSStest in the same manner as in Example 21. The results are shown in Table5.

Reference Example

Without irradiating the disk having formed thereon a hydrogenatedcarbonaceous protective layer in the same manner as in Example 21 withultraviolet rays, a layer having a thickness of 12 Å, 15 Å, or 18 Å wasformed on the respective disk surfaces by immersing in a chloroformsolution containing 4,4'-diaminodibenzo-18-crown-6 in a concentration of2 mmol/l (0.781 g/l).

The resulting disk was immersed in a chloroform for 5 minutes and wasraised at a rate of 2 mm/s. The results showed that the coated layer hadhardly remainder adhered to the disk surface.

Example 25

The same disk as used in Example 1 was immersed in a chloroformcontaining copper stearate and 1,4,8,11-tetraazacyclo-tetradecane, eachin a concentration of 1 mmol/l to form an even lubricant layer having athickness of 16 Å on the disk surface.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. The results are shown in Table 2.

Example 26

The same disk as used in Example 1 was immersed in a mixture of waterand methanol containing silver acetate andN,N'-dibenzyl-4,13-diaza-18-crown-6, each in a concentration of 1 mmol/lto form a coated layer having a thickness of 6 Å on the disk surface.Then, to the resultant disk using a chloroform solution containingβ-(N,N-diheptadecylaminocarbonyl)propionic acid in a concentration of 2mmol/l, a lubricant layer having a total thickness of 19 Å was formed.

The disk on which the lubricant layer was formed was subjected to alubricating performance test and a cohesion test in the same manner asin Example 1. The results are shown in Table 2.

                                      TABLE 1                                     __________________________________________________________________________                  Spindle test   CSS test                                                Initial                                                                              Residual thickness of                                                                        torque                                                  thickness of                                                                         lubricant layer (%)                                                                          (gf · cm)                                      lubricant                                                                            1  4   7   14  Initiation of                                                                       During                                            layer (Å)                                                                        day                                                                              days                                                                              days                                                                              days                                                                              rotation                                                                            sliding                                    __________________________________________________________________________    Example 3                                                                            25     81 71  71  67  28    11                                         Example 4-1                                                                          26     85 82  81  79                                                   Example 4-2                                                                          24                    35     8                                         Example 5                                                                            44     84 79  78  75  --    --                                         Example 6                                                                            18     80 79  79  78  --    --                                         Comparative                                                                          20     67 57  57  52  --    --                                         Example 4                                                                     Comparative                                                                          31     76 71  68  65                                                   Example 5-1                                                                   Comparative                                                                          27                    50     8                                         Example 5-2                                                                   Comparative                                                                          41     72 69  67  64  --    --                                         Example 6                                                                     Comparative                                                                          21     76 59  53  45                                                   Example 7-1                                                                   Comparative                                                                          16                    64    25                                         Example 7-2                                                                   __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________           Thickness of                                                                  lubricant layer                                                                       Friction                                                              (Å) force (gf)                                                                          Cohesion (25° C./40% RH)                                                            Head                                        __________________________________________________________________________    Example 1                                                                            29      1.6   None > 32 days                                                                             a                                           Example 2                                                                            45      2.1   None > 32 days                                                                             a                                           Example 7                                                                            21      3.5   None > 35 days                                                                             b                                           Example 8                                                                            33      2.9   None > 35 days                                                                             b                                           Example 9                                                                            33      2.8   None > 35 days                                                                             b                                           Example 10                                                                           26      2.8   None > 35 days                                                                             b                                           Example 13                                                                           49      1.6   None > 32 days                                                                             a                                           Example 14                                                                           28      1.8   None > 32 days                                                                             a                                           Example 25                                                                           16      3.8   None > 14 days                                                                             b                                           Example 26                                                                           19      3.0   None > 14 days                                                                             b                                           Comparative                                                                          13      2.7   Observed < 3 days                                                                          a                                           Example 1                                                                     Comparative                                                                          16      1.4   Observed < 3 days                                                                          a                                           Example 2                                                                     Comparative                                                                          28      3.4   Observed < 3 days                                                                          b                                           Example 3                                                                     __________________________________________________________________________     Head:                                                                         a: MnZn Ferrite                                                               b: Al.sub.2 O.sub.3.TiC                                                  

                  TABLE 3                                                         ______________________________________                                        Thickness of   Friction  Friction                                             lubricant layer                                                                              force after                                                                             force after 2                                        (Å)        10 min (gf)                                                                             hr (gf)    Head                                      ______________________________________                                        Example 11                                                                            17         --        3.5      b                                       Example 12                                                                            31         --        2.9      b                                       Example 15                                                                            17         1.8       2.0      a                                       Example 16                                                                            16         2.0       2.0      a                                       Example 17                                                                            24         1.1       1.1      a                                       Comparative                                                                           13         2.0       2.7      a                                       Example 1                                                                     Comparative                                                                           28         3.1       3.4      b                                       Example 3                                                                     Comparative                                                                           25         1.8       Wear     a                                       Example 8                                                                     ______________________________________                                         Head:                                                                         a: MnZn ferrite                                                               b: Al.sub.2 O.sub.3.TiC                                                  

                  TABLE 4                                                         ______________________________________                                               Thickness of                                                                  lubricant layer                                                                         Friction* Cohesion                                                  (Å)   force (gf)                                                                              (60° C./80% RH)                             ______________________________________                                        Example 18                                                                             23          3.6       None (>15 days)                                Example 19                                                                             32          3.8       None (>15 days)                                Example 20                                                                             50          3.4       None (>15 days)                                Comparative                                                                            28          3.4       Observed (<1                                   Example 9                      day)                                           ______________________________________                                         *Head: Al.sub.2 O.sub.3.TiC                                              

                  TABLE 5                                                         ______________________________________                                        CSS test*                 Cohesion                                            Stain                  Torque     test                                        on head       Initiation                                                                             during     (25° C./40% RH)                      and disk      torque   sliding    after 14 days                               ______________________________________                                        Example 21                                                                            None       9 gfcm   7 gfcm  None                                      Example 22                                                                            None      23 gfcm  11 gfcm  None                                      Example 23                                                                            None       9 gfcm   9 gfcm  None                                      Example 24                                                                            None      21 gfcm  11 gfcm  None                                      Comparative                                                                           None      65 gfcm  17 gfcm  --                                        Example 10                                                                    ______________________________________                                         *Head: Al.sub.2 O.sub.3.TiC                                              

As is evident from the results shown in Table 2, it was confirmed thatcohesion was observed on the lubricant layer of Comparative Examples 1to 3 in which a lubricant alone was used, while such cohesion wasprevented on the lubricant layer of Examples 1 and 2 according to thepresent invention even if the thickness thereof was thicker than thoseof Comparative Examples 1 to 3 (being slightly thicker due to thepresence of the host layer). It was further found that the lubricantlayer of Examples 1 and 2 had a lubricating performance and a drivingperformance comparable or superior to those of the systems containing alubricant alone according to Comparative Examples 1 to 3.

Further, the orientation of the alkyl chain in the lubricant layerprepared in Example 2 was analyzed by FTIR-RAS. As a result, as shown inFIG. 8, the CH stretching vibration attributed to a methyl group at thetip of the alkyl chain was clearly observed. It was also confirmed thatthe alkyl chain was oriented in such a good state as to be verticallyoriented against the substrate since the intensity of the CH stretchingvibration of the methylene chain was comparatively small.

Taking into account the layer thickness, it is considered that thebinding site on the lubricant layer was oriented to the substrate andthe layer is a mono layer having a structure such that the alkyl chainwas arranged with being directed upward (FIG. 1), which is almost anoptimal structure as a lubricant layer. On the contrary, in theconventional system composed of a lubricant(β-(N,N-diheptadecylaminocarbonyl)propionic acid) alone (ComparativeExample 3), the intensity of absorbance based on the CH stretchingvibration of the methyl group at the tip of the alkyl chain was smalland the intensity of the CH stretching vibration of the methylene chainwas large. Thus, it was found that the orientation of the alkyl chain onthe disk was so poor that the alkyl chains were oriented in differentdirections.

From the results shown in Table 1, it was confirmed that, in thelubricant layer according to the present invention, even in the casewhere a liquid lubricant was used, the spin-off of the lubricantmolecule was effectively prevented and the adhesion of the head asobserved in the case of using a liquid lubricant hardly occurred. Thatis, in the lubricating system according to the present invention, such aspin-off was effectively prevented by having the lubricant compoundadhered to the substrate using the host-guest complex lubricant layer.In addition, the fixation and lubricating performance did not use atradeoff and the lubricant layer was constituted so as to have anexcellent lubricating performance and a durability while hardlyundergoing any adhesion.

When, on the one hand, a liquid lubricant, perfluoropolyether, wasdirectly coated on a smooth disk (Comparative Examples 5 and 7), it isconsidered that the lubricant migrates on the surface and collects atthe true contact region between the head and the disk to form a meniscusdue to the low interaction between the lubricant and the surface of theprotective layer. On the other hand, in the case in which a liquidlubricant was fixed on the smooth substrate using a host-guest complex(Examples 3 and 4), the torque at the initiation of rotation was loweredto 35 gf·cm or less.

From the results of Examples 7 to 10, it was confirmed that thelubricant layer formed using a multidentate ligand having a function totrap a metal ion, a metal compound, and a lubricating molecule having anactive hydrogen independently as a material had an excellent lubricatingperformance and the cohesion of the lubricant molecule was prevented,similar to the lubricant layer formed by using the lubricant molecule,which had been isolated and purified as an alkaline metal salt, as aguest compound.

As shown in the results of Examples 13 and 14, it was found that thelubricant layer prepared by forming the multidentate ligand layer andthen forming the lubricant molecule layer exhibited a lubricatingperformance comparable or superior to that of the lubricant layer fixedby using a solution in which the lubricant molecule and crown ether hadformed the host-guest complex (Example 2). It is considered that, ineach case, the fixed host-guest complexes have a layer constitution suchthat the crown ether, which strongly interacts with the substrate as awhole, adheres to the surface of the disk and the lubricant molecule iscoordinated thereon.

As is clear from the results shown in Table 3, it was found that thelubricant composed of potassium stearate and dibenzo-18-crown-6(Examples 15 and 16) exhibited a more excellent lubricating performancethan the lubricant composed of only potassium stearate according toComparative Example 1. Further, it was found that the lubricant composedof stearylamine and dibenzo-18-crown-6 (Example 17) maintained anexcellent lubricating performance for a long period of time as comparedto the layer of Comparative Example 8, which resulted in wear.

The lubricant composed of β-(N,N-diheptadecylaminocarbonyl)propionicacid and 4,4'-diaminodibenzo-18-crown-6 (Example 2) showed a lubricatingperformance at the initial sliding stage comparable or superior toComparative Example 3 in whichβ-(N,N-diheptadecylaminocarbonyl)propionic acid was used alone. Thelubricating performance of Comparative Example 3 decreased considerablyafter 2 hours of continuous sliding, as compared to Examples whichretained excellent lubricating performance at the initial stage withalmost no change. Further, the coated layer of Comparative Example 3readily became uneven, while the coated layer of Example 2 had notbecome uneven even after one month or more.

Effect of the Invention

The present invention provides a reliable lubricating system which is athin layer having almost the same layer thickness as a mono layer withan excellent lubricating performance and abrasion resistance. In thecase of the solid lubricant, the cohesion of the lubricant molecule canbe prevented and, in the case of the liquid lubricant, an excellentdurability can be maintained for a long period of time because of theprevention of spin-off. When using a smooth substrate to lower the liftof the head, adhesion to the head, which is inherent in the liquidlubricant, does not occur and a satisfactory lubricating performance andsufficient durability can be maintained. There is no problem ofcohesion, which is inherent in the solid lubricant. When the lubricantlayer is applied to a magnetic recording medium, the data recordingdensity can be increased and a magnetic recording medium with long-termreliability can thus be obtained.

We claim:
 1. A lubricant layer which comprises a host-guest complexformed by a host compound which is a multidentate ligand having afunction to reversibly trap a metal ion or an organic ion byelectrostatic interaction and a guest compound, said host compound beingcoated on a solid surface.
 2. The lubricant layer according to claim 1,wherein said host compound contains three or more atoms of at least oneelement selected from the group consisting of oxygen, nitrogen, andsulfur.
 3. The lubricant layer according to claim 2, wherein said hostcompound is a cyclic multidentate ligand and corresponding donor atomscontain a lone electron pair having an sp³ hybrid orbital.
 4. Thelubricant layer according to claim 1, wherein said metal ion to betrapped by the host compound is used as a guest compound in combinationwith a lubricant molecule having a terminal functional group which formsan ionic pair together with the metal ion.
 5. The lubricant layeraccording to claim 1, wherein said guest compound is a compound having amolecular structure bearing a lubricating function and a basic terminalgroup.